The effect of polymerization shrinkage during veneer placement.

: This study evaluated the relationship of polymerization shrinkage during composite resin veneer placement to direction of the polymerization light source. Fifty maxillary permanent incisors were obtained and divided into five groups of ten. Groups I and II had preparations placed in enamel. Groups III, IV, and V had preparations placed in dentin. In groups I and III, an unfilled bonding resin was placed and polymerized from the facial aspect, followed by placement and polymerization of a hybrid composite resin. Groups II and IV were initially polymerized from the lingual direction. In group V, the unfilled resin and hybrid composite resin were polymerized simultaneously from the facial aspect. Statistical analysis indicated that there was significantly less axial microgap formation during lingual polymerization when the preparation remained in dentin, but demonstrated that there was no statistically significant difference when the preparation remained in enamel.